The normal operating temperature of the HO2S(Heated Oxygen Sensor) ranges from 350 to 850°C(662 to 1562°F). The HO2S heater greatly decreases the amount of time required for fuel control to become active. The ECM provides a pulse width modulated control circuit to adjust current through the heater. When the HO2S is cold, the value of the resistance is low and the current in the circuit is high. On the contrary, if the temperature in the resistor of the sensor rises, the current drops gradually.
Checking current from HO2S under detecting condition,if the heater current is below a certain threshold for more than predeterminate time, PCM sets P0155. MIL(Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycle.
Item
Detecting Condition
Possible cause
DTC Strategy
? Monitor the current through the heater
? Poor Connection
? HO2S(B2/S1)
? PCM
Enable Conditions
? Engine Running > 60 sec.
? Heater Duty Cycle > 40%
? Max. Duty Cycle - Min. Duty Cycle < 5%
Threshold value
? Filtered Heater Current < threshold value
Diagnosis Time
? Continuous (More than 2.5 second failure for every 5 second test )
MIL On Condition
? 2 Driving Cycles
Condition
Current(A)
Heater Current at 13.5V, 450?(842°F) Exhaust
0.52 ± 0.1
The HO2S requires a minimum temperature to provide a closed loop fuel control system. So the HO2S contains a heater element to reduce its warm-up time and ensure its performance during all driving conditions. The PCM controls this heater element by duty cycle. The main relay supplies voltage to the heater and the PCM provides a ground circuit for activating the heater.